Lightly dust your work surface with icing sugar, then roll out a quarter of the black fondant icing to the thickness of a £1 coin. Cut out two triangles for the ears and leave to dry overnight.
Heat oven to 160C/140C fan/gas 3. Butter and line a 20cm round cake tin (about 7.5cm deep). Put the dark chocolate in a medium pan with the butter. Mix 1 tbsp coffee granules into 125ml cold water and add to the pan. Warm over a low heat until just melted – don’t let it boil. Alternatively, melt in the microwave for about 5 mins, stirring halfway through.
Mix the flour, bicarb and sugar with the cocoa powder. Beat the eggs with the milk. Pour the melted chocolate mixture and the egg mixture into the flour mixture and stir everything together to make a smooth batter.
Pour the batter into the tin and bake for 1 hr 25-1 hr 35 mins until a skewer inserted into the centre of the cake comes out clean and the top feels firm (don’t worry if it cracks a bit). Leave to cool in the tin for 30 mins – the top may sink a little as it cools – then turn out onto a rack to cool completely. Cut the cake horizontally into three.
To make the frosting, put the butter in a bowl and beat until light and fluffy. Gradually beat in the icing sugar and cocoa powder, then stir in enough milk to make the icing fluffy and spreadable. Sandwich the layers of the cake together using a small amount of frosting. Melt the chocolate in a microwave or small bowl set over a pan of simmering water, then stir it into the remaining frosting. Use the mixture to cover the sides and the top of the cake.
Stick the black fondant ears into the top of the cake. Cut out two yellow or orange fondant circles to make the eyes and use the black fondant to make the pupils. Stick these onto the cake and add a heart-shaped jelly sweet for the nose. Use Pocky sticks, Matchmakers or liquorice cut into lengths for the whiskers.